Packaging pressure-sensitive adhesives



Patented Apr. 20, 1954 ,1 1-1;

PACKAGING PRESSURE-SENSITIVE 1 ADHESIVES Warner Eustis, Newton, Mass, assignor to The Kendall Company, Boston, Mass., a corporation of Massachusetts No Drawing. Application April 8, 1953, Serial No. 347,629

9 Claims. (01. 206-84) This invention relates to packaging of pressure-sensitive adhesive tapes comprisin polyrnerizable systems, this application being a continuation-in-part of my copending application Serial No. 214,444, which is a division of my once co-pending application now issued as Patent No. 2,572,458, which in turn was a continuation-inpart copending with my earlier filed application Serial No. 380,013, filed February 21,1941, and now abandoned, which patent and applications, excepting Serial No. 214,444, were directed, at least in part, to pressure-sensitive adhesive tapes per so, as well as to the method of packaging the same, and the packaged tapes to which Serial No. 214,444 is directed and which are herein claimed.

One of the objects of this inventiondisclosed in said Patent No. 2,572,458 is the provision of an adhesive tape which carries a coating of a viscous tacky'composition consisting essentially of polymeric styrene, the composition having characteristics such that it may be preserved over substantial periods of time in a soft, viscous, tacky, pressure-sensitive condition, preferably in a prepared container, untilready for use, at which time the tacky coated tape may be ma:- nipulated and applied to an external surface in the ordinary manner of masking or of surgeons tape. 7

Another object of the invention, not confined to pressure-sensitive adhesive tapes consisting essentially of polymeric styrene, is the provision of other packaged tapes containing adhesives comprising polymerizable, systems which, similarly to styrene, are coated on suitable backings and similarly converted into tapes which are suitably preserved in proper packaging and which, upon being removed from the package, may be applied to an external surface whereupon the adhesives further polymerize in a manner similar to partially polymerized polystyrene composition jadhesives.

As described in said Patent No. 2,572,458, I

have discovered that polystyrene adhesiv may be prepared by partially polymerizing a quantity of monomeric styrene, and then dissolving the partially polymerized composition, which is at a predeterminedly controlled degree of polymerization, in a further quantity'of styrene-'-either monomeric styrene or polymeric styrene at a 'lower degree of polymerization, or mixtures thereofand which second quantity of' styrene contains a styrene polymerization inhibitor or retarding agent.' Such i'ngredients'may be formulated so that the composition has suitable viscosity for "spreading on'a backing and sothat 2 further polymerization will be' definitely controlled with the adhesive retaining sticky, tacky characteristics over substantial periods of time after spreading, by proper packaging, whereby, upon removal fromthe package, the coating will be fresh, soft and tacky, as is required for classi fication as a pressure-sensitive adhesive, and will remain so at room temperatures for a period sufiiciently long to permit manipulation of the coated backing as a flexible pressure-sensitive adhesive tape with application in the customary manner to electrical or other parts, to which the tape will conform by reason of its flexibility.

After application, the tape may remain soft and tacky for a further period, depending upon the particular typ and amount of inhibitor included. In the usual case, however, the polymerization retarding effect of the inhibitor will be overcome in the course of exposure to atmospheric oxygen and other environmental influences over a period of time with resulting gradual polymerization into a dry mass. Such final setting up of the adhesive to form in some cases a bond between the backing and theartitale to which th tape has been applied, may if desired be accelerated by application of heat and/or by the inclusion in the adhesive mass of oxygen catalysts, preferably those becoming active at elevated temperature. 7

I have further discovered that a whole group of polymerizable systems, of which styrene is only a part, maybe utilized for making tapes, which tapes, though initially pressure-sensitive, eventually lose their pressure-sensitive character through polymerization. These tapes, which normally display various degrees of adhesiveinstability, may be preserved in their pressuresensitive conditionby means of proper packaging in the presence of stabilizers and inhibitors.

Tapes comprising such polymerizable systems may, in addition to the partially polymerized polymer, contain resins, fillers and compounding agents in the nature of softening or tackifying agents, plasticizers, adhesive strength enhancers and reinforcing or diluting fillers, without departing from the scope of the invention.

In general, the pol-ymerizable systems which areuseful in the packaged pressure-sensitive ad hesives of this invention comprise vinyl systems which proceed by free radical polymerization and which under normal atmospheric conditions continue to advance in polymerization at a too rapid rate to maintain usable pressure-sensitive, qualities over normal shelf life periods, such polymerizable systems include polymers, copolymers and terpolymers of the following compounds:

(a) Aryl vinyl compounds, such as styrene, pchloro styrene, p-methyl styrene, alpha-methylp-methyl styrene, and meta-chloro styrene; (b) heterocyclic vinyl compounds, such as vinyl pyridine, vinyl thiophene, vinyl carbazole and vinyl pyrolle; alkyl divinyl compounds, such as butadiene, 2,3-dimethyl butadiene, 2-methyl butadiene, 2-chloro butadiene, and ZA-dimethyl penta-l, 3-diene; (:1) alkyl vinyl compounds, such as copolymerized isobutylene; (c) vinyl esters, such as vinyl acetate; (3) acrylic compounds, such as methyl acrylate, ethyl acrylate, butyl aorylate, isobutyl acrylate; (g) derivatives 1 of alpha, beta-unsaturated, alpha, beta-dicarboxylic acids (copolymers only), such as methyl maleate, ethyl maleate, butyl maleate, hexyl :nialeate, fumaric acid esters of alcohols which contain less than six carbon atoms, aconitic and itaconic esters of alcohols which contain less than six carbon atoms, and mono alkyl esters of alphabeta unsaturated alpha-beta dicarboxylic .1 acids; and (h) vinyl etherssuch as vinylalkyl'eth'ers from ethyl through butyl.

-Resinous materialsingeneral which are suitable and compatible-With any of the polymerizable. systemsabove described may be incorporated into the adhesives.forthepurposeof modifying tack .and plasticity or promoting adhesive strength. Those which Iprefer include rosin, hydrogenated rosin, disproportionated rosin, rosin esters, hydrogenated rosin esters, disproportionated rosin esters, polyterpenes, and alkyl substituted phenol-formaldehyde resins condensed in-the presence of rosin and its derivatives.

Finelygrouncl .inert materials are generally suitable as reinforcing and diluting fillers and pigments, but I prefer pulverized hard polymeric material of the same general type as that used in the adhesive, or finely ground mica, ground silica, ground glass, alumina, hydrated magnesium, aluminum silicate, fine-particle silicon dioxide, whiting, ground limestone, precipitated .calcium carbonate, barytes, lithopone, titanium 'dioxide,.zinc oxide. or carbon black.

For some purposes, it maybe desirable toadd various plasticizers and softeners to obtain re" .quisite characteristics in the tape, either in the pressure-sensitive or the fully polymerized convdition. Where that is the case, I prefertouse high boiling petroleum fractions such as are used'in-rubber processing or the alkyd resins in general, but other compatible plasticizers and softeners maybe utilized if desired.

As examples of typical preparations of ad- .hesives of this invention, I set forth thefollow- .ing:

Example I Seventy-two .parts of styrenemonomer .are polymerized at 125 C. fora periodof approximately 3 hours, then cooled as rapidly as possible and mixed with 22% parts of styrene monomer. vSince styrene monomer'is unstable, the above operations may be advantageously conducted in a nitrogen atmosphere. This composition has a viscosity suitable for doctor spreading on any suitable sheet backing, for instance, of glass, polystyrene, polybutene or polyethylene. In order, however, to maintain stability, it is advantageous to incorporate in the mix .05% of a styrene polymerizationv inhibitor in the form of hydroquinone, or equivalent amounts of quinone, benzoquinoneor phenanthraquinone.

The composition as appliedwill have soft, sticky, tacky characteristics and will .be transparent.

Where the coating is to be thin, the spreading operation is also advantageously conducted in the absence of oxygen. Application of the coating may be to one or both sides of the backing, a: or by an impregnating operation, the supporting medium, if of the porous type like woven glass fabric, can be provided with a pressuresensitive tacky adhesive on both sides. Whether the operation be one of coating or of impregnatlo"ing,:azthincontinuous flexible film of the composition may be secured. In some cases volatile hydrocarbon solvents may be resorted to as thinners *orrliluents for the purpose of spreadinglthecompositions on the backing.

Again ground or pulverized solid polymeric -'styrene'.'or:any one of the several hard varieties of polystyrene, finely ground mica, ground silica (quartz), ground glass, or combinations thereof may be included as inert fillers.

Since some partially polymerized adhesive sy..- terns, particularly styrene; polymerize eventuah lyeven-inthe-darkand in;the absence of heat and oxygen, certain precautions are required in packaging the tapes of "this tinvention where 25 storageover'long periods prior to use is contemplated. While for some conditions it is sufii- 'cient'topackage the tape'in an'air=tight, light tight container, under other conditions .it' is: ad-

vantageous to reduce or eliminate atmospheric oxygen-by evacuating partially, atileast,"air from the containenor to "fill the container with a fluid such as a vaporiorgas whichis inert toward, i. e., will not positively catalyze, the'polymerization, examples of gases 'beingnitrogen, carbon dioxide, helium, argon, krypton, Xenon and the chloroefluoro vmethanes. Where qualities permitting storage formaximum time periods are required, instead of using agas which merely is inactive so far as the polymerization reaction is 40 concerned, it may befounddesirable to introduce a gas of a type whichof'itselftends to inhibit polymerization. The gaseous hydrocarbonsisobutane, butylene and propane are useful for this purpose, being mildly inhibitive. 'In

"either case the fluid is catalytically negative'toward the polymerization.

' Suitable'gases more strongly'inhibitiveof polymerization of the adhesives of'this invention include hydrogen sulfide, ammonia and nitrous oxide. Suitable vapors of volatile liquids which are strongly inhibitive include butyraldoxime,

acetaldehyde, formaldehyde, vglyoxal, n-alkyl mercaptans such as ethyl and propyl, concentrated aqueous ammonia and amines of the type represented by the formula:

where R is methyl or ethyl andRz and R3 are methyl or hydrogen.

Example II The following mixture:

Parts by weight Butadiene Styrene 30 Water 180 Disproportionated rosin soap 5 70 Potassium persulfate 0.5 Potassium chloride 0.3

'Sodiumialkylnaphthalene sulfonate 2 'Mixed'hexyl mercaptans 0.05 Mixedoctyl mercaptans 0.05 .Mixed'tertiary mercaptans (C12+C14) 10.05

" to evaporate.

isemulsified in a suitable pressure vessel and heated for 3 hours at 120 F. Thereafter, the vessel is opened and the excess butadiene allowed To this latex, consisting of an abnormal mixture of mixed molecular weight polymers and unreacted styrene monomer, is added a blend of 5 parts styrene monomer and; 1 part ethyl amine. The blend is then slowly stirred for'several hours to allow the dispersed styrene and ethyl amine to diffuse into the polymer particles.

Such a dispersion which may be thickened by a suitable agent, such as carboxymethyl cellulose, is coated onto'fibrous backing materials in the well-known manners. Following drying through an oven, the coated web is slit and rolled into tape form. To prevent further polymerization during storage, the tape roll is packaged in a hermetically sealed can containing additionalpolymerization inhibitor such as ethyl amine, or nitrogen.

When required for use, the tape. is removed from the can, applied to the desired surface or object effectively by means of its pressure-sensitive character, and the ethyl amine allowed to evaporate undernormal conditions or accelerated by slight heating; Thereafter the interrupted polymerization resumes through the action of residual catalyst and the effect of oxygen in the air to yield a non-pressure-sensitive, semi-solvent resistant, adhesive bonded structure.

Example III A mixture of 50 parts ethyl acrylate and 50 parts of dibutyl maleate is dissolved in 250 parts of acetone. Following addition of 0.1 part of benzoyl-peroxide, the mixture was refluxed for minutes at which time 0.05 part of hydroquinone was added and the reaction mixture cooled rapidly to interrupt the polymerization. Following concentration, through partial in vacuo removal of the acetone, the viscous blend was ground on a paint mill with 5 parts carbon black, 5 parts ultra-fine particle size calcium carbonate and 5 parts of the glycerol ester of wood rosin (ester gum). To this was added a. mixture of 5 parts butyl acrylate, 0.5 part of benzoyl peroxide and 0 .5 parts of an inhibitor butyraldehyde oxime.

A woven web, comprised of cellulosic fibers, was impregnated and coated with the above mixture through dipping and subsequent removal of excess material by doctor-knife technique. The impregnated and coated web was carried through a drying chamber where residual solvent was removed. Following this operation, the pressuresensitive adhesive coated web was adhered to an interliner, slit into tape and wound into rolls. The resultant tape rolls carrying an inhibited partially polymerized adhesive were packaged in hermetically sealed cans.

In use, the tape is removed from the can and applied to the desired surface. Followingv evaporation of the temporary inhibitor thesystem will'resume polymerization upon completion of which a tack-free, rigid, highly reinforced bond, between'theadhesive and the surface of application, results. Application of heat, through infrared heaters, chemical hot-packs, etc., may be used to accelerate the settin time if that is desired.

Example IV Fifty (50) parts of allyl methacrylate are dissolved in two hundred (200) parts of chloroform and the whole heated at reflux for two hours in the presence of 1.0 parts of benzoyl peroxide.

6 The resulting viscous solution of polymer is then coated onto a suitable woven web or other backing by a simple knife coater and the coated web slit into tape rolls of the desired width and length. Said rolls are then sealed in hermetically sealed cans under positive pressure of mm. of hydrogen sulfide.

Following storage, the pressure-sensitive coated web may be applied to the surface to be covered whereupon the adhesive further polymerizes to a non-tacky, rigid, immobile, solvent and heat resistant structure which result may be accelerated by spraying with diethyl etherate of boron trifluoride.

Example V A mixture of ninety-eight (98) parts of maleic anhydride and one hundred and seven (10'?) parts of vdiethylene glycol are heated with stirring in the presence of a trace of litharge under a blanket of carbon dioxide at 200 C. until the acid number is ten or less. Following cooling to 50 C., 73 parts of styrene monomer (in which .05 part of hydroquinone has been dissolved) are added. A woven web of glass fabric is then dip-coated with the mixture, slit intotape form and stored in a hermetically sealed can with methyl-ethyl amine.

In application, the tape is removed from the can, the methyl-ethyl amine evaporates'and the tape is applied in the desired manner, after which polymerization will occur through action of the light and oxygen of the atmospheric environment. This polymerization may be greatly accelerated by quickly dipping the tape (just prior to use) in a solution of 20 parts styrene, 2 parts of benzoyl peroxide and 0.'1 part cobalt naphthenate.

- Example VI A mixture of1100- parts butyl acrylate in 250 parts benzene is heated to. reflux with stirring. To this boiling mixture is added 0.75 partof benzoy1peroxide. After reacting for 0.5 hour, an additional 0.7.5 part of benzoyl peroxide is added, and the reaction refluxed for an additional two hours. Following cooling to room temperature 0.3 part of butyraldehyde oxime is added. The mixture is then dip-coated onto a non-woven cellulosic web, slit into tape and stored in a hermetically sealed can.

In application, the tape is removed from the can, aflixed in the desired location and polymerization is allowed to proceed through volatilization of the inhibitor and action of environmental heat and light.

Example VII A mixture of 100 parts butyl acrylate in 250 parts of carbon tetrachloride is heated to reflux with stirring. At time intervals of 0.5 hour, 1.5 parts of benzoyl peroxide are added until a total of 6.0 parts catalyst have been used. After an additional two hours refluxing, the solution is concentrated by distilling off the bulk of the carbon tetrachloride while stirring.

100 parts of the inhibited polymer of Example VI are combined with 50 parts of the above concentrated polymer solution, and the resultant solution of high and low molecular weight polymers is dip-coated onto a cellulosic web and con verted into tape.

parties, maybe-established through suitable-com trol of certain variables. Among these, is the degree of preliminary polymerization which dependsupon the temperature and duration and/or catalyst of the initial polymerization reaction. Again,-where more than one molecular weight is involved, the viscosity and consistency of the mass-may be controlled by varying the degree of polymerization of the polymer of lower-degree of polymerization to be added, and by properly proportioning its amount or the amount of -mnomeric material or mixtures thereof which ;is' to beaddedrto the preliminarily polymerized :portion. In some cases other suitable solvents may be resorted to as thinners or diluents for the purposes of spreading the'compositions on the backing, bras carriers for :the polymerization controllingagent or agents. For instance, iethylbenzeneor benzene may-be of value with styrene. Onthe other hand, the'consistency may-bemodifled. in direction of greater viscosity by resorting to a vacuum distillation at .low temperature :of the initially partially polymerizedbatch, there by removing a portion of the monomer-which remains after the preliminary polymerization.

.Also, the amount of inhibitor included should be based upon the length :of time and conditions of storage contemplated for the finished tape.

t room temperatures, the adhesives of this invention in their pressure-sensitive state have viscosities running from to about-10 and preferably from 10 to 10 poises. After application .;the adhesives normally will polymerize to solid. state viscosities higher than 10 poises.

As will beseen, the coatedtapesof this-inven tion having supporting backings either .of glass, cloth,.paper, or of other suitablesheet materials, fibrous or non-fibrous, find highly advantageous use in electrical work, for instance as wire insulation for making electrical joints, or for other insulating purposes where a tape with a high dielectric strength is required. .In addition, such tapes, even aside from their electricalproperties, have other highly desirable properties. both .before and after final polymerization, including high resistance to heat, acids, alkaliesiand solvents.

A further desirable use for the .tapes of this invention'is as a foundation backing or supporting medium for pressure-sensitive or .other adhesive coatings of well-known types 50 that the coatings of this invention .act either as priming coats or as repellent coatings oras'both. Where it acts, as a primingcoat, the .compositionmay be either in its pressure-sensitive orin its dry flexible state at or after application of the additional coating. In these uses the transparent character of some of the coatings of this invention permits theiravailability asbackings in the formation of transparent tapes.

Havingthus described my invention, what I claim'is:

1. A packaged pressure-sensitive adhesive comprising a container having sealed .thereina soft, tacky pressure-sensitive adhesive consisting essentially of a polymericmaterial normally-advancing in polymerization anda fluid content which is inert toward polymerization of; saidmaterial for preserving the pressure-sensitive qualities of the packaged adhesive.

2. A. packaged pressure-sensitive adhesive comprising a container having sealedutherein a soft, tacky pressure-sensitive adhesive. consisting essentially of a polymericmaterial. normally advancing, in polymerizationand a gaseouscontent which is inerttowardpolymerization:ohsaidmaterial for preserving the pressure-sensitive:qualities of the packaged-adhesive.

3. A packaged pressure-sensitive adhesive comprising a container having sealed therein a soft, tacky pressure-sensitive adhesive consisting essentially of a polymeric material normally-advancing "in-polymerization and a fluid content which inhibits polymerization of said material for preserving the pressure-sensitive qualities of the packaged adhesive.

l. -A packaged pressure-sensitive adhesive comprising a container having sealed therein a soft, tacky pressureesensitive adhesive consisting essentially .of partially polymerized styrene at a predetermined incomplete and intermediate stage of polymerization, said container having therein a gaseous styrene polymerization retarding agent for maintaining the pressure-sensitive qualities of the packaged adhesive.

5. .A packaged pressure-sensitive tape comprising a container having sealed therein a flexible backing bearing a coating of asoft, tacky pressure-sensitive adhesive consisting. essentially of a polymeric material normally advancing in polymerization and a fluid content which is catalytically negative toward polymerization of said material for maintaining the pressure-sensitive qualities of the adhesive coating-of the packaged tape.

6. A packaged pressure-sensitive tape as claimed in claim 5 wherein'the fluid content includes an inhibitor to said normallyadvancing polymerization.

'7. A packaged pressure-sensitive tape comprising a container having sealed therein a flexible backing bearing a coating of a soft, tacky pressure-sensitive adhesive consisting essentially of partially polymerizer styrene at a predetermined incomplete and intermediate stage-of polymerization, said container having therein a gaseous styrene polymerization retarding agent formaintaining the pressure-sensitive qualities of the adhesive coating of the packaged tape.

-.8..The method of purposefully providing a pressure-sensitive adhesive which will lose its pressure-sensitive adhesive qualities after useful application toan external surface, comprising formulating anadhesive having pressure-sensi-- tive adhesive qualities and containing as-an essential constituent a polymerizable vinyl material which norrnally advances in polymerization to harden saidadhesive, and packaging said adhesive in a sealed container, the fluidcontent of which is inert towards polymerization of said material, to maintain the .pressureesensitive qualities of said adhesive pending use.

.9. The method of purposefully providing .a pressure-sensitive adhesive which will lose its pressure-sensitive adhesive qualities after useful application to an external surface, comprising formulatingan adhesive having pressureesensitive adhesive qualities and containing as, an essential constituent a polymerizable vinyl material which normally advances in polymerizaton to harden said adhesive, and packagingsaid adhesive in a sealed container, the. fluidcontent of which inhibits polymerization of, said material, to maintain the pressure-sensitive qua1ities of said adhesive pending use.

No references cited. 

4. A PACKAGE PRESSURE-SENSITIVE ADHESIVE COMPRISING A CONTAINER HAVING SEALED THEREIN A SOFT, TACKY PRESSURE-SENSITIVE ADHESIVE CONSISTING ESSENTIALLY OF PARTIALLY POLYMERIZED STYRENE AT A PREDETERMINED INCOMPLETE AND INTERMEDIATE STAGE OF POLYMERIZATION, SAID CONTAINER HAVING THEREIN A GASEOUS STYRENE POLYMERIZATION RETARDING AGENT FOR MAINTAINING THE PRESSURE-SENSITIVE QUALITIES OF THE PACKAGED ADHESIVE. 